The impact of the herbicide diuron on photosynthesis in three species of tropical seagrass

The impact and recovery from exposure to the herbicide diuron [DCMU; 3-(3',4'-dichlorophenyl)-1,1-dimethylurea] was assessed for three tropical seagrasses, maintained in outdoor aquaria over a 10-day period. Photosynthetic stress was detected using chlorophyll a fluorescence, measured with a Diving-PAM (pulse amplitude modulated fluorometer). Exposure to 10 and 100 pg l(-1) diuron resulted in a decline in effective quantum yield (F/F-m') within 2 h of herbicide exposure in Cy-modocea serrulata, Halophila ovalis and Zostera capricorni. Effective quantum yield also declined over the first 24 h of exposure in H. ovalis at even lower diuron concentrations (0.1 and 1.0 mug l(-1)). Effective quantum yield in H. ovalis and Z. capricorni was significantly depressed at all diuron concentrations (0.1-100 mug l(-1)) after 5 days exposure, whereas effective quantum yield in C. serrulata was only significantly lower in plants exposed to highest diuron concentrations (10 and 100 mug l(-1)). Effective quantum yield depression was present 5 days after plants exposed to 10 and 100 mug l(-1) diuron were returned to fresh seawater. These results indicate that exposure to herbicide concentrations present in nearshore Queensland sediments present a potential risk to seagrass functioning. (C) 2000 Elsevier Science Ltd. All rights reserved.